There are many different types of antennas designed for operation with RF (radio frequency) communication systems. Many such antennas exhibit gain and directivity characteristics that make them particularly suitable for specific applications.
Requirements for gain and directivity are often dictated by coverage desired in a particular application. For a conventional community repeater installation, as is well-known in the art, an antenna system having an omnidirectional pattern is most often utilized. Of course, terrain features or man-made obstructions can influence antenna choice, and a directional antenna is often employed when the desired coverage area is irregular in shape, or it is impossible to deploy an antenna near the center of the desired coverage area.
Cellular telephone systems often prove particularly challenging to antenna designers and system planners alike. Since most cellular systems were initially deployed in urban areas, most system planners have had to contend with obstructions in one or more cells due to tall buildings. These types of obstructions generally give rise to irregularly shaped cells and/or antenna deployment in areas outside the cell center.
Obstructions are in part responsible for some of the anomalous signal propagation that is characteristic of the 800 MHz (megahertz) spectrum. Other propagation difficulties are created by frequency-selective fading, multipath, and doppler effect, as is well-known in the art. Cell sectoring and diversity are often used to help combat these problems.
In cell sectoring, a cell is divided into sectors of 120 degrees, for example (60 degree sectors are also used). Antennas with selected gain/directivity characteristics are used to cover selected sectors of a cell. Usually, these sector antennas are used for receiving by the cell site, with an omnidirectional antenna used for transmitting throughout the cell. A dedicated transmitting antenna can also be used for each sector.
At least two types of diversity are also used to improve cell site performance. Spatial diversity can be implemented by positioning two receive antennas, physically displaced from one another, for each cell site. If one antenna is subject to a fading phenomenon, the other antenna may not be.
Polarization diversity is also a popular tool. In polarization diversity, two cell site antennas are provided in each sector for receiving, with each antenna having a different polarization (one vertical and one horizontal, for example, or one circular and one linear). One antenna per sector is generally provided for transmitting.
In order to take advantage of both spatial and polarization diversity in a sectored cell, an antenna system is required that possesses the requisite polarization and directivity characteristics. The horizontal beam width should be extendable to 120 degrees to ensure adequate coverage in each sector of a three-sector cell. Accordingly, a need arises for a horizontally polarized antenna array providing extended horizontal beam width. The antenna array should be easily combined with a vertical array to create a composite antenna, and should be durable, easily mountable, and relatively economical to manufacture.